Caption: Light micrograph showing conjugating filaments of Spirogyra sp., a green alga which forms slimy threads in stagnant or slow moving water. Conjugation, a form of sexual reproduction, occurs in spring when the threads come together in pairs. Both filaments put out papillae, which meet to form conjugation tubes. Cytoplasmic mass from the cells of one of the threads (termed male) migrates through the tubes to fuse with the cytoplasm in the (female) cells of the second thread. This produces zygospores, the green ovoids seen here, which either germinate at once or lie dormant until the following spring. Magnification: x200 at 35mm size.